Boron-containing compounds including borates, boric acids, and boric oxides are well known for use as antiseptics pesticidal, and preservative uses. U.S. Pat. No. 1,911,551 is directed to an insect repellant and the following U.S. Patents are directed to various types of boron-containing materials used for destroying household insects such as ants, cockroaches, termites, and the like.
______________________________________ 496,110 1,757,222 4,944,950 4,996,053 1,029,203 4,363,798 4,959,221 5,464,613 ______________________________________
U.S. Pat. Nos. 1,635,461 and 2,968,590 disclose the use of boron-containing compounds to preserve fruit after harvesting and prevent the growth of fungus.
U.S. Pat. Nos. 360,700; 890,636; 907,498; 1,923,004; 1,976,905; and 3,012,931 show the use of various types of boron-containing materials for protecting plant vegetation such as trees by destroying insects and fungus that would adversely effect the foliage, flower, and fruit.
Japanese Patent Application No. 571982! - 47,903 and the following U.S. patents disclose the use of boron-containing compounds as wood preservatives before and after harvesting.
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U.S. Pat. No. 4,291,497 discloses the application of boron as a trace element in powder form onto plants being treated.
U.S. Pat. Nos. 711,367; 2,773,757; 3,531,278; and 3,560,381 show various types of boron-containing compositions used as herbicides. U.S. Pat. Nos. 2,770,538 and 3,674,458 show the use of boron-containing compounds as fertilizers.
As is known, the use of boron-containing materials as herbicides and insecticides for plant vegetation is very critical. Boron toxicity in agricultural use constitutes an important agricultural problem because natural soils may contain too much boron or be irrigated with water containing excessive concentrations of the element or boron fertilizers that are applied in excessive amounts. The management of soils regarding the amount of boron is difficult because the range between the deficient and toxic level of the element is known to be narrow. On the one hand, boron-containing compounds are useful on plants as insecticides to preserve vegetation. However, if too much boron is applied to the plant, it will be damaged. This is particularly a problem in products such as tobacco where the leaf itself is the product being harvested.
In the article "Some Considerations About the Tolerance of Various Plant Species to Excessive Supplies of Boron", Soil Science, 92:243-247 (1961), researchers J. J. Oertli and H. C. Kohl of the University of California examine the time necessary to produce boron toxicity symptoms with ten parts per million (ppm) in solution, and boron concentrations in leaves of various plant species. This article is incorporated herein in its entirety by reference to explain the known factors related to this fundamental problem in handling boron-containing materials such as borates.
Boron-containing pesticides are not for general use in the agricultural industry on field crops because no viable delivery system exists that will provide pesticidal characteristics without adversely affecting the leaf. In addition, available delivery systems do not maintain the pesticide in contact with the vegetation long enough to provide pesticidal effectiveness over an extended period of time. These problems are particularly true of insecticides. Environmental conditions such as the amount of rainfall, volatilization of the active ingredient, and wind conditions all adversely effect the potential use of boron-containing compounds for general agricultural use.
Various known delivery systems for pesticides in powder, solid, and liquid forms include liquid formulations such as emulsions, colloidal suspensions, organic and aqueous solutions containing the borons as shown in the various U.S. patents referenced herein. The following U.S. patents show various delivery systems used for pesticides.
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U.S. Pat. Nos. 5,526,181 and 5,435,821 disclose controlled or slow release formulations having active chemical agents coated with polymers including encapsulated boron-containing micronutrient. Basic problems relate to polymer encapsulation of agricultural fertilizers and pesticides, however. Moreover, nothing in these patents show the use of boron-containing compounds as pesticides and more specifically, as insecticides.
Commercially Available Pesticides
Other commercially known pesticides such as herbicides, fungicides, insecticides, bactericides and other active agents and compounds are applied periodically in the home, agriculture, and other places and can be dangerous to humans. Farmers, however, still need to spray their crops and animals with these active agents and compounds. To this end, there have been several unsuccessful attempts to provide a method of delivering these compounds in a manner that is safe, effective, and economical, as well as environmentally acceptable.
Various encapsulating techniques have been tried with agricultural active agents with results considered insufficient to justify replacement of existing agricultural formulations. Nothing in the prior art either suggests, teaches, or discloses the use of liposomal microencapsulation techniques to active agents such as pesticides in agricultural formulations.
Liposomal microencapsulation is known in the pharmaceutical industry and has five steps. Ethanol (95%) is mixed in a particular proportion with high grade soybean lecithin containing 50% phosphatidylcholine (PC). The ethanol soybean lecithin mixture is agitated until the PC and other soluble portions of the lecithin have been dissolved into the ethanol. The mixture is then allowed to stand for a period of time, so that the insoluble portions can settle to the bottom of the container, and the top becomes a clear amber color. The top portion is then drawn off and saved. The bottom sludge is discarded. A certain amount of water is added to the mixture, followed by a predetermined amount of ethanol.
The steps followed up to this point result in a basic "stock" solution that is mixed with an active agent (AA) of choice in the pharmaceutical industry. The next step is the addition of a preselected AA to the stock solution. The final step is to then add the preselected AA solution to water, thereby effecting formation of the microcapsules or vesicles.
This known pharmaceutical method is limited to the use of 95% ethanol as a solvent and a high grade (50% PC) granular soybean lecithin as the only lipid source. This procedure produces a dilute solution of lecithin because of the low amount of lecithin used and the addition of extra ethanol and water. This is acceptable in the medical field because dose rates are very low, thus requiring low loading potentials. This known process is not acceptable in other fields, however, which require higher loading potentials such as in agricultural formulations used for pesticides.
Ethanol is the only solvent that is usable in the pharmaceutical industry and that is a problem in many agricultural applications, because not all agricultural compounds are soluble in ethanol. Furthermore, ethanol is a highly flammable solvent, and expensive EPA regulations on the proper packaging of flammable materials make ethanol impractical to use in most agricultural uses necessitating a less flammable solvent system. For these reasons, there is no suggestion in the pharmaceutical use of ethanol to use ethanol in agricultural formulations.
The mere extraction of lecithin from animal sources such as egg yolks does not relate to the agricultural industry. Japanese Patent No. C87-154187 discloses the extraction of lecithin from egg yolks. It states that the uses and advantages are for food, drugs and toiletries. Japanese Patent Nos. C88-116693 and C89-086119 disclose methods of further extraction and purification of phosphatidylcholine (PC) from egg lecithin. These patents disclose the use of egg lecithin as an emulsifier for food, drugs, and toiletries, but do not suggest making liposomes or liposomal carrier systems. These Japanese patent references specify a method of extraction and purification of PC from egg lecithin.
As determined in the pharmaceutical industry, animal or egg lecithin contains a higher percentage of saturated fatty acid side chains, which impart a more rigid gelatinous quality to resulting liposomes when used for liposomal encapsulation of drugs. In turn, there is a slower, more extended release rate of the entrapped drugs. This characteristic is advantageous for drug delivery systems but is not desirable in agricultural applications of pesticides where there may be a risk of causing chemical residue problems.
The average price for high purity (99%) animal PC at $75.00 per 100 milligrams is $340,194.00 per pound. The average price for high purity (99%) egg PC at $76.00 per 100 milligrams is $34,473.00 per pound. Low purity (60%) PC egg PC at $0.68 per 100 milligrams is $308.44 per pound. Soybean lecithin with PC content between twenty percent (20%) to forty percent (40%) can be purchased for under $10.00 per pound.
Canadian Patent No. 834,472 discloses the process of extracting PC from crude vegetable oils using monoglycerides to aid the process. This reference discloses varying the levels of the monoglycerides and different ways of using the monoglycerides in the process. The reference does not mention, suggest, teach, or disclose liposome formation or, more specifically, liposomal encapsulation of active agents for agricultural uses. Its use is strictly for food additives, bakery uses, cosmetics, and a one word mention of a medical use.
Active agents of particular interest in the agricultural industry are pesticides, which is a generic term for herbicides, fungicides, bactericides, and insecticides. Other agricultural active agents include dyes and stains. It has been discovered in this invention that the key to encapsulating such active agents for agricultural applications is the amphipathic material known as lecithin and, more specifically, plant lecithin.
Plant Lecithin
In the American Oil Chemists' Society book entitled Lecithins and edited by Bernard F. Szuhaj and Gary R. List, at page 289, author Y. Pomeranz states that the "term `lecithin` is the commercial or popular name for a naturally occurring mixture of similar compounds more accurately identified as phosphatides or phospholipids. The principal components of the natural mixture are phosphatidylcholine, phosphatidylethanolamine, inositol phosphatides and related phosphorus-containing lipids."
At page 1 of the book, Lecithins, author C. R. Scholfield says that "I!n modern usage, lecithin generally refers to a complex, naturally occurring mixture to phosphatides obtained by water-washing crude vegetable oil and separating and drying the hydrated gums. In addition to the phosphatides, such products contain triglycerides and other substances that are removed in an emulsion with gums. Soybean lecithin, the most common commercial product, has been reported to contain 25-35% triglycerides and smaller amounts of other nonphosphatide materials."
Commercially available plant lecithin is composed of the phospholipids called phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), and phosphatidic acid (PA), carotenoid, and, depending on the grade of the plant lecithin, varying levels of oils, triglycerides, fibrous materials and, in some cases, additives and surfactants. Commercial lecithins are available in dry granular, liquid, gel, paste, and powder forms.
The invention is limited to the use of plant lecithins as contrasted with animal lecithins that are obtained from animal sources such as egg yolks. As is well known, plant lecithins are found in soybean oil, cottonseed oil, canola oil, wheat oil, kelp, peanuts, and sunflower seeds.
At pages 185-188 and 195 of the book Lecithins published in 1985, authors J. C. Schmidt and F. T. Orthoefer discuss nonfood uses of lecithin. A known miscellaneous function of lecithin is as a liposomal encapsulating agent. Among nonfood applications, however, lecithin is used as a liposomal encapsulating agent only in the pharmaceutical industry. The authors discuss agricultural and agriproduct processing uses of lecithin with a particular small section concerning pesticides.
Nothing in the book, Lecithins, teaches, discloses, or suggests the use of plant lecithin as the key to using liposomal encapsulating techniques for encapsulation of active agents such as pesticides for agricultural applications. Moreover, there is nothing in any prior art to suggest, teach, or disclose the liposomal encapsulation of active agents for agricultural applications.
It is known that pharmaceuticals and drugs are applied in low doses such as in milligrams and parts per million for human consumption. In comparison, pesticides are applied in known quantities measured in terms of pounds of active agent per acre of crop. All commercially available agricultural chemicals such as pesticides have known formulations for effecting their desired results. Some known pesticides contain as much a 48% and even up to 72% active agent in their known formulations.
The pharmaceutical application of lecithin, consequently, does not offer any help in using plant lecithin as a liposomal encapsulating agent in agricultural applications that require loading high concentrations of active agent into the initial stock solution composition of the invention. For example, the initial stock solution used in pharmaceutical applications uses a very low lipid content so that large amounts of active agent cannot be loaded into it.
It is known that PC is the material in plant lecithin that actually does the encapsulating in the liposomal microencapsulation process. The molecule of PC has a phosphate head with a choline moiety and some fatty acid chains that form a tail portion. The fatty acid chains are nonpolar and therefore repel water. The phosphate head of the PC molecule attracts water. When placed in water, the molecules coalesce so that the molecule tails are directed one way and the heads another to produce the vesicle formation of the liposomal encapsulation technique.